This invention relates to a method of producing hollow profiles from multilayer starting materials, such as woven fabrics, knitted fabrics, laid materials, webs or the like, having a large width-to-thickness ratio, in a continuous process. The invention also relates to hollow profiles which are produced in accordance with the method of the invention, the form of which is determined by features of the production process.
Methods of producing hollow profiles from multilayer woven fabrics, laid materials, knitted fabrics or webs are known wherein these starting materials are shaped by being drawn onto mandrel-shaped tools or other shaping tools along with the occurrence of sliding friction. The cross-sectional geometry of the shaping tool or tools then determines the clear cross-section of the hollow profile which is produced or rather of the channels in the hollow profile which is produced.
Also known are processes for manufacturing hollow profiles in which the shaping is effected by pressure impingement on the channels or pockets which are already formed in the starting materials. The expansion and the final geometric shape of the hollow profiles can, in such cases, possibly also be influenced by external limitations. In the case of starting materials having an open surface, i.e. one permeable to gas and liquid, it is known to employ the latter method by introducing thin-walled foil tubes or sleeves into the channels or pockets of the starting materials, upon production or subsequently, to enable their expansion by pressure impingement thereon. After the shaping process is completed, these inserts can remain as "lost cores" in the hollow profiles or they can be removed.
In the various known methods, just mentioned, it is also known to wet or to impregnate the starting materials prior to or during the shaping process with a matrix, such as a synthetic resin or plastics material, and to cause this matrix, after shaping of the hollow profile structure has been effected, to harden, e.g. by the supply of heat, and thus to stiffen this structure.
The known methods can be used to produce hollow profiles which have only one coherent cavity (hollow space) or profiles which have several separate cavities.